Birefringence optical film

ABSTRACT

The present invention provides a birefringent optical film that allows a liquid crystal display to achieve excellent contrast and a wide viewing angle and does not cause coloring of the liquid crystal display. The birefringent optical film includes at least one birefringent A-layer having a property satisfying ny a ≧nz a &gt;nx a  or nz a &gt;ny a &gt;nz a  and at least one birefringent B-layer having a property satisfying nx b ≧ny b &gt;nz b .

TECHNICAL FIELD

The present invention relates to a birefringent optical film.

BACKGROUND ART

Conventionally, in order to allow a liquid crystal display to achieveexcellent contrast, a biaxial birefringent optical film has been used asa retardation plate. In general, a biaxial birefringent optical film isproduced by stretching an isotropic polymer film (see Patent Documents 1and 2, for example).

Also, by stretching a uniaxial polymer film (see Patent Document 3, forexample), it is possible to produce a biaxial birefringent optical film(see, Patent Document 4, for example). A liquid crystal displayincorporating such a biaxial birefringent optical film can achieveexcellent contrast. However, since the And values exhibited by thebiaxial birefringent optical film are in only a narrow limited range,wide viewing angles in accordance with various mode types have not yetbeen realized sufficiently by the use of the biaxial birefringentoptical film. Moreover, there has been a problem in that displaycoloring may be caused in a liquid crystal display, e.g., a VA modeliquid crystal display, incorporating the biaxial birefringent opticalfilm.

-   Patent Document 1: JP 3(1991)-33719 A-   Patent Document 2: JP 3(1991)-24502A-   Patent Document 3: JP 8(1996)-511812 A-   Patent Document 4: JP 2000-190385 A

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

It is an object of the present invention to provide a birefringentoptical film that allows a liquid crystal display to achieve excellentcontrast and a wide viewing angle and does not cause coloring of theliquid crystal display.

Means for Solving Problem

The present invention provides a birefringent optical film including atleast one birefringent A-layer and at least one birefringent B-layer.The birefringent A-layer has a property satisfying ny_(a)≧nz_(a)>nx_(a)or nz_(a)>. ny_(a)>nx_(a), and the birefringent B-layer has a propertysatisfiing nx_(b)>ny_(b)>nz_(b).

It is to be noted that nx_(a), ny_(a) and nz_(a) respectively representrefractive indices in an X-axis direction, a Y-axis direction, and aZ-axis direction in the birefringent A-layer, with the X-axis directionbeing an axial direction that is the same as a below-mentioned X-axisdirection of the birefringent B-layer, the Y-axis direction being anaxial direction that is the same as a below-mentioned Y-axis directionof the birefringent B-layer, and the Z-axis direction being a thicknessdirection perpendicular to the X axis and the Y axis.

It also is to be noted that nx_(b), ny_(b) and nz_(b) respectivelyrepresent refractive indices in the X-axis direction, the Y-axisdirection, and a Z-axis direction in the birefringent B-layer, with theX-axis direction being an axial direction exhibiting a maximumrefractive index within a plane of the birefringent B-layer, the Y-axisdirection being an axial direction. perpendicular to the X axis withinthe plane, and the Z-axis direction being a thickness directionperpendicular to the X axis and the Y axis.

EFFECTS OF THE INVENTION

By using the birefringent optical film of the present invention, it ispossible to allow a liquid crystal display to achieve excellent contrastand a wide viewing angle and also to allow coloring of the liquidcrystal display to be prevented from occurring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing an example of wavelength dispersioncharacteristics of a birefringent A-layer and a birefringent B-layerincluded in an optical film of the present invention.

FIG. 2 is a graph showing an example of wavelength dispersioncharacteristics (reciprocal wavelength dispersion) of an optical film ofthe present invention.

DESCRIPTION OF THE INVENTION

A birefringent optical film according to the present inventionconfigured so as to include the above-described two types ofbirefringent layers exhibits a broad range of And values, so that it canrealize a wide viewing angle of a liquid crystal display. In particular,with regard to some kinds of liquid crystal displays whose opticalcharacteristics could not be compensated by conventional birefringentoptical films, it becomes possible to realize a wide viewing angle bythe use of the birefringent optical film of the present invention.

Furthermore, the birefringent optical film of the present inventionexhibits sufficiently large Rth values, so that it allows a liquidcrystal display to achieve excellent contrast.

Moreover, the birefringent optical film of the present invention doesnot cause coloring when incorporated in a liquid crystal display.

In the birefringent optical film of the present invention, thebirefringent B-layer preferably meets a requirement represented by aformula (1) below.0.005≦Δn_(b)≦0.2  (1)

In the formula (1), Δn_(b) is nx_(b)−nz_(b), and nx_(b) and nz_(b)respectively represent the refractive indices in the X-axis directionand the Z-axis direction in the birefringent B-layer, with the X-axisdirection being the axial direction exhibiting the maximum refractiveindex within the plane of the birefringent B-layer and the Z-axisdirection being the thickness direction perpendicular to the X-axis.

In the birefringent optical film of the present invention, thebirefringent A-layer may be formed of at least one of a polymerexhibiting negative birefringence and a polymer exhibiting positivebirefringence. Alternatively, the birefringent A-layer may be formed ofa mixture of a polymer exhibiting negative birefringence and a polymerexhibiting positive birefringence.

In the birefringent optical film of the present invention, thebirefringent B-layer may be formed of a polymer exhibiting positivebirefringence.

Preferably, the polymer exhibiting positive birefringence is at leastone polymer selected from the group consisting of polyamide, polyimide,polyester, polyetherketone, polyaryletherketone, polyamide imide andpolyesterimide

Preferably, the birefringent optical film of the present invention meetsa requirement represented by a formula (4) below.−3°≦alignment axis accuracy≦3°  (4)

Note here that the alignment axis accuracy refers to variation in slowaxis within a plane of the birefringent optical film.

In the birefringent optical film of the present invention, it ispreferable that an in-plane retardation of the birefringent optical filmas a laminate has reciprocal wavelength dispersion characteristics.

Preferably, the birefringent optical film of the present invention meetsrequirements represented by formulae (5) and (6) below.|Δnd_(a)|>|Δnd_(b)|  (5)α_(a)≦α_(b)  (6)

In the formulae (5) and (6),

-   -   Δnd_(a)=(nx_(a)−ny_(a))·d_(a),    -   Δnd_(b)=(nx_(b)−ny_(b))·d_(b),    -   Δ_(a)=Δnd_(a430 nm)/Δnd_(a550 nm), and    -   Δ_(b)=Δnd_(b430 nm)/Δnd_(b550 nm).

It is to be noted that nx_(a) and ny_(a) respectively represent therefractive indices in the X-axis direction and the Y-axis direction inthe birefringent A-layer, with the X-axis direction being the axialdirection that is the same as the X-axis direction of the birefringentB-layer and the Y-axis direction being the axial direction that is thesame as the Y-axis direction of the birefringent B-layer, and darepresents a thickness of the birefringent A-layer.

It also is to be noted that nx_(b) and ny_(b) respectively represent therefractive indices in the X-axis direction and the Y-axis direction inthe birefringent B-layer, with the X-axis direction being the axialdirection exhibiting the maximum refractive index within the plane ofthe birefringent B-layer and the Y-axis direction being the axialdirection perpendicular to the X-axis within the plane, and dbrepresents a thickness of the birefringent B-layer.

It also is to be noted that Δnd_(a430 nm) and Δnd_(a550 nm) respectivelyrepresent Δnd_(a) values of the birefringent A-layer at wavelengths of430 nm and 550 nm.

It also is to be noted that Δnd_(b430 nm) and Δnd_(b550 nm) respectivelyrepresent Δnd_(b) values of the birefringent B-layer at the wavelengthsof 430 nm and 550 nm.

A laminated polarizing plate according to the present invention is alaminated polarizing plate including a birefringent optical film of thepresent invention.

A liquid crystal panel according to the present invention is a liquidcrystal panel including a liquid crystal cell and an optical member. Inthe liquid crystal panel, the optical member is disposed on at least onesurface of the liquid crystal cell and the optical member is a laminatedpolarizing plate of the present invention.

A liquid crystal display of the present invention is a liquid crystaldisplay including a liquid crystal panel of the present invention.

An image display according to the present invention is an image displayincluding a birefringent optical film of the present invention or alaminated polarizing plate of the present invention.

In the present invention, it is necessary that the birefringent A-layerhas a property satisfying ny_(a)≧nz_(a)>nx_(a) or nz_(a)>ny_(a)>nx_(a).The reason for this is that the birefringent A-layer with such aproperty can reduce light leakage in oblique directions effectively whenit is incorporated in an image display.

Preferably, the birefringent A-layer with such a property is formed of apolymer exhibiting negative birefringence, a polymer exhibiting positivebirefringence, or a mixture of a polymer exhibiting negativebirefringence and a polymer exhibiting positive birefringence. Morepreferably, the birefringent A-layer is formed of a polymer exhibitingnegative birefringence or a mixture of a polymer exhibiting negativebirefringence and a polymer exhibiting positive birefringence.

Note here that the polymer exhibiting negative birefringence refers to apolymer that forms a polymer film exhibiting a minimum refractive indexin a stretching direction when it is stretched.

The polymer exhibiting negative birefringence may be a homopolymer basedon a single monomer such as polystyrene, an acrylic substance, orpolymethyl methacrylate. Alternatively, a copolymer of such ahomopolymer and one or more other polymers may be used as the polymerexhibiting negative birefringence, in order to improve a mechanicalproperty of the resultant film. Generally known examples of such acopolymer include styrene-maleic anhydride copolymers, styrene-maleimidecopolymers, copolymers including an olefin unit and an acrylic substanceunit, and copolymers including a nitrile unit and a styrene unit.Examples of the nitrile compound include: α-substituted unsaturatednitrile such as acrylonitrile and methacrylonitrile; and nitrilecompounds including an α,β-disubstituted olefine-type unsaturated bondsuch as fumaronitrile. On the other hand, the styrene compound may be anunsubstituted or substituted styrene compound, such as styrene,vinyltoluene, methoxystyrene, chlorostyrene or α-methylstyrene.

Note here that the polymer exhibiting positive birefringence refers to apolymer that forms a polymer film exhibiting a maximum refractive indexin a stretching direction when it is stretched.

The polymer exhibiting positive birefringence may be a resin based onacetate, polyester, polyethersulfone, polycarbonate, polyamide,polyimide, polynorbornene, polyolefin, polyethylene oxide, orpolyphenylene ether. Alternatively, in order to improve a heatresistance and/or a mechanical strength of the resultant film, acopolymer including an alkene unit in combination with a substituted orunsubstituted maleimide unit or a substituted or unsubstituted vinylunit can be used as the polymer exhibiting positive birefringence.Examples of such a copolymer include an olefin-maleimide copolymer.

It is preferable that the polymer exhibiting positive birefringence is anon-liquid crystal polymer such as polyamide, polyimide, polyester,polyetherketone, polyamide imide, polyesterimide, or the like because ofits excellent heat resistance, chemical resistance, transparency, andhardness. It may be possible to use one of these non-liquid crystalpolymers alone or a mixture of two or more polymers having differentfunctional groups, for example, a mixture of polyaryletherketone andpolyamide. Among these non-liquid crystal polymers, polyimide isparticularly preferable because of its high transparency, high aligningproperty, and high stretching property.

The molecular weight of the non-liquid crystal polymer is notparticularly limited, but the weight-average molecular weight (Mw)thereof preferably ranges from 1,000 to 1,000,000 and more preferablyranges from 2,000 to 500,000.

As the polyimide, it is preferable to use a polyimide that has a highin-plane aligning property and is soluble in an organic solvent.Specifically, examples of such a polyimide include a condensationpolymer product of 9,9-bis(aminoaryl) fluorene and an aromatictetracarboxylic dianhydride disclosed in JP 2000-511296 A, i.e., apolymer containing at least one repeating unit represented by thegeneral formula (1) below.

[Chemical Formula 1]

In the above general formula (1), R³ to R⁶ are at least one substituentselected independently from the group consisting of a hydrogen atom, ahalogen atom, a phenyl group, a phenyl group substituted with 1 to 4halogen atoms or a C₁₋₁₀ alkyl group, and a C₁₋₁₀ alkyl group.Preferably, R³ to R⁶ are at least one substituent selected independentlyfrom the group consisting of a halogen atom, a phenyl group, a phenylgroup substituted with 1 to 4 halogen atoms or a C₁₋₁₀ alkyl group, anda C₁₋₁₀ alkyl group.

In the above general formula (1), Z is, for example, a C₆₋₂₀quadrivalent aromatic group, and preferably is a pyromellitic group, a.polycyclic aromatic group, a derivative of a polycyclic aromatic group,or a group represented by the general formula (2) below.

[Chemical Formula 2]

In the general formula (2) above, Z′ is, for example, a covalent bond, aC(R⁷)₂ group, a CO group, an O atom, an S atom, an SO₂ group, anSi(C2H₅)₂ group, or an NR⁸ group. When there are plural Z's, they may bethe same or different. Also, w is an integer from 1 to 10. R⁷sindependently are hydrogen or C(R⁹)₃. R⁸ is a hydrogen atom, an alkylgroup having from 1 to about 20 carbon atoms, or a C₆₋₂₀ aryl group, andwhen there are plural R⁸s, they may be the same or different. R⁹sindependently are a hydrogen atom, a fluorine atom, or a chlorine atom.

The above-mentioned polycyclic aromatic group may be, for example, aquadrivalent group derived from naphthalene, fluorene, benzofluorene, oranthracene. Further, a substituted derivative of the above-mentionedpolycyclic aromatic group may be the above-mentioned polycyclic aromaticgroup substituted with at least one group selected from the groupconsisting of, for example, a C₁₋₁₀ alkyl group, a fluorinatedderivative thereof, and halogen atoms such as an F atom and a Cl atom.

Other than the above, homopolymer whose repeating unit is represented bythe general formula (3) or (4) below or polyimide whose repeating unitis represented by the general formula (5) below disclosed in JP8(1996)-511812 A may be used, for example. The polyimide represented bythe general formula (5) below is a preferable mode of the homopolymerrepresented by the general formula (3).

[Chemical Formula 3]

In the above general formulae (3) to (5), G and G′ each are a groupselected independently from the group consisting of, for example, acovalent bond, a CH₂ group, a C(CH₃)₂ group, a C(CF₃)₂ group, a C(CX₃)₂group (wherein X is a halogen atom), a CO group, an O atom, an S atom,an SO₂ group, an Si(CH₂CH₃)₂ group, and an N(CH₃) group, and G and G′may be the same or different.

In the above general formulae (3) and (5), L is a substituent, and d ande indicate the number of substitutions therein. L is, for example, ahalogen atom, a C₁₋₃ alkyl group, a halogenated C₁₋₃ alkyl group, aphenyl group, or a substituted phenyl group, and when there are pluralLs, they may be the same or different. The above-mentioned substitutedphenyl group may be, for example, a substituted phenyl group having atleast one substituent selected from the group consisting of a halogenatom, a C₁₋₃ alkyl group and a halogenated C₁₋₃ alkyl group. Also, theabove-mentioned halogen atom may be, for example, a fluorine atom, achlorine atom, a bromine atom, or an iodine atom. d is an integer from 0to 2, and e is an integer from 0 to 3.

In the above general formulae (3) to (5), Q is a substituent, and findicates the number of substitutions therein. Q may be, for example, anatom or a group selected from the group consisting of a hydrogen atom, ahalogen atom, an alkyl group, a substituted alkyl group, a nitro group,a cyano group, a thioalkyl group, an alkoxy group, an aryl group, asubstituted aryl group, an alkyl ester group and a substituted alkylester group and, when there are plural Qs, they may be the same ordifferent. The above-mentioned halogen atom may be, for example, afluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Theabove-mentioned substituted alkyl group may be, for example, ahalogenated alkyl group. Also, the above-mentioned substituted arylgroup may be, for example, a halogenated aryl group. f is an integerfrom 0 to 4, and g and h respectively are an integer from 0 to 3 and aninteger from 1 to 3. Furthermore, it is preferable that g and h arelarger than 1.

In the above general formula (4), R¹⁰ and R¹¹ are groups selectedindependently from the group consisting of a hydrogen atom, a halogenatom, a phenyl group, a substituted phenyl group, an alkyl group, and asubstituted alkyl group. It is particularly preferable that R¹⁰ and R¹¹independently are a halogenated alkyl group.

In the above general formula (5), M¹ and M² may be the same or differentand, for example, a halogen atom, a C₁₋₃ alkyl group, a halogenated C₁₋₃alkyl group, a phenyl group, or a substituted phenyl group. Theabove-mentioned halogen atom may be, for example, a fluorine atom, achlorine atom, a bromine atom, or iodine. The above-mentionedsubstituted phenyl group may be, for example, a substituted phenyl grouphaving at least one substituent selected from the group consisting of ahalogen atom, a C₁₋₃ alkyl group, and a halogenated C₁₋₃ alkyl group.

A specific example of polyimide represented by the general formula (3)includes polyimide represented by the general formula (6) below.

[Chemical Formula 4]

Moreover, the above-mentioned polyimide may be, for example, copolymerobtained by copolymerizing acid dianhydride and diamine other than theabove-noted skeleton (the repeating unit) suitably.

The above-mentioned acid dianhydride may be, for example, aromatictetracarboxylic dianhydride. The aromatic tetracarboxylic dianhydridemay be, for example, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, naphthalene tetracarboxylic dianhydride,heterocyclic aromatic tetracarboxylic dianhydride, or 2,2′-substitutedbiphenyl tetracarboxylic dianhydride.

The pyromellitic dianhydride may be, for example, pyromelliticdianhydride, 3,6-diphenyl pyromellitic dianhydride,3,6-bis(trifluoromethyl) pyromellitic dianhydride,3,6-dibromopyromellitic dianhydride, or 3,6-dichloropyromelliticdianhydride. The benzophenone tetracarboxylic dianhydride may be, forexample, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride,2,3,3′,4′-benzophenone tetracarboxylic dianhydride, or2,2′,3,3′-benzophenone tetracarboxylic dianhydride. The naphthalenetetracarboxylic dianhydride may be, for example,2,3,6,7−naphthalene-tetracarboxylic dianhydride,1,2,5,6−naphthalene-tetracarboxylic dianhydride, or2,6-dichloro-naphthalene-1,4,5,8-tetracarboxylic dianhydride. Theheterocyclic aromatic tetracarboxylic dianhydride may be, for example,thiophene-2,3,4,5-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride, orpyridine-2,3,5,6-tetracarboxylic dianhydride. The 2,2′-substitutedbiphenyl tetracarboxylic dianhydride may be, for example,2,2′-dibromo-4,4′,5,5′-biphenyl tetracarboxylic dianhydride,2,2′-dichloro-4,4′,5,5′-biphenyl tetracarboxylic dianhydride, or2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl tetracarboxylicdianhydride.

Other examples of the aromatic tetracarboxylic dianhydride may include3,3′,4,4′-biphenyl tetracarboxylic dianhydride,bis(2,3-dicarboxyphenyl)methane dianhydride,bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,4,4′-bis(3,4-dicarboxyphenyl)-2,2-diphenylpropane dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride, 4,4′-oxydiphthalicdianhydride, bis(3,4-dicarboxyphenyl)sulfonic dianhydride,3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride,4,4′-[4,4′-isopropylidene-di(p-phenyleneoxy)]bis(phthalic dianhydride),N,N-(3,4-dicarboxyphenyl)-N-methylamine dianhydride, andbis(3,4-dicarboxyphenyl)diethylsilane dianhydride.

Among the above, the aromatic tetracarboxylic dianhydride preferably is2,2′-substituted biphenyl tetracarboxylic dianhydride, more preferablyis 2,2′-bis(trihalomethyl)-4,4′,5,5′-biphenyl tetracarboxylicdianhydride, and further preferably is 2,2′-bis(trifluoromethyl)4,4′,5,5′-biphenyl tetracarboxylic dianhydride.

The above-mentioned diamine may be, for example, aromatic diamine.Specific examples thereof include benzenediamine, diaminobenzophenone,naphthalenediamine, heterocyclic aromatic diamine, and other aromaticdiamines.

The benzenediamine may be, for example, diamine selected from the groupconsisting of benzenediamines such as o-, m-, and p-phenylenediamine,2,4-diaminotoluene, 1,4-diamino-2-methoxybenzene,1,4-diamino-2-phenylbenzene, and 1,3-diamino-4-chlorobenzene. Examplesof the diaminobenzophenone may include 2,2′-diaminobenzophenone and3,3′-diaminobenzophenone. The naphthalenediamine may be, for example,1,8-diaminonaphthalene or 1,5-diaminonaphthalene. Examples of theheterocyclic aromatic diamine may include 2,6-diaminopyridine,2,4-diaminopyridine, and 2,4-diamino-S-triazine.

-Further, other than the above, the aromatic diamine may be4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl methane,4,4′-(9-fluorenylidene)-dianiline,2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl,3,3′-dichloro-4,4′-diaminodiphenyl methane,2,2′-dichloro-4,4′-diaminobiphenyl, 2,2′,5,5′-tetrachlorobenzidine,2,2-bis(4-aminophenoxyphenyl)propane, 2,2-bis(4-aminophenyl)propane,2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 4,4′-diaminodiphenyl ether, 3,4′-diamino diphenyl ether,1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3,-hexafluoropropane,4,4′-diamino diphenyl thioether, or 4,4′-diaminodiphenylsulfone.

The polyetherketone may be, for example, polyaryletherketone representedby the general formula (7) below, which is disclosed in JP 2001-49110 A.

[Chemical Formula 5]

In the above general formula (7), X is a substituent, and q is thenumber of substitutions therein. X is, for example, a halogen atom, alower alkyl group, a halogenated alkyl group, a lower alkoxy group, or ahalogenated alkoxy group, and when there are plural Xs, they may be thesame or different.

The halogen atom may be, for example, a fluorine atom, a bromine atom, achlorine atom, or an iodine atom, and among these, a fluorine atom ispreferable. The lower alkyl group preferably is a C₁₋₆ lower straightchain alkyl group or a C₁₋₆ lower branched chain alkyl group and morepreferably is a C₁₋₄ straight or branched chain alkyl group, forexample. More specifically, it preferably is a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a sec-butyl group, or a tert-butyl group, and particularlypreferably is a methyl group or an ethyl group. The halogenated alkylgroup may be, for example, a halide of the above-mentioned lower alkylgroup such as a trifluoromethyl group. The lower alkoxy group preferablyis a C₁₋₆ straight or branched chain alkoxy group and more preferably isa C₁₋₄ straight or branched chain alkoxy group, for example. Morespecifically, it further preferably is a methoxy group, an ethoxy group,a propoxy group, an isopropoxy group, a butoxy group, an isobutoxygroup, a sec-butoxy group, or a tert-butoxy group, and particularlypreferably is a methoxy group or an ethoxy group. The halogenated alkoxygroup may be, for example, a halide of the above-mentioned lower alkoxygroup such as a trifluoromethoxy group.

In the above general formula (7), q is an integer from 0 to 4. In thegeneral formula (7), it is preferable that q=0 and a carbonyl group andan oxygen atom of an ether that are bonded to both ends of a benzenering are present at para positions.

Also, in the above general formula (7), R¹ is a group represented by thegeneral formula (8) below, and m is an integer of 0 or 1.

[Chemical Formula 6]

In the above general formula (8), X′ is a substituent and is the same asX in the general formula (7), for example. In the general formula (8),when there are plural X's, they may be the same or different. q′indicates the number of substitutions in the X′ and is an integer from 0to 4, preferably, q′=0. In addition, p is an integer of 0 or 1.

In the general formula (8), R² is a divalent aromatic group. Thisdivalent aromatic group is, for example, an o-, m-, or p-phenylene groupor a divalent group derived from naphthalene, biphenyl, anthracene, o-,m-, or p-terphenyl, phenanthrene, dibenzofuran, biphenyl ether, orbiphenyl sulfone. In these divalent aromatic groups, hydrogen that isbonded directly to the aromatic may be substituted with a halogen atom,a lower alkyl group, or a lower alkoxy group. Among them, the R²preferably is an aromatic group selected from the group consisting ofthe general formulae (9) to (15) below.

[Chemical Formula 7]

In the above general formula (7), the R′ preferably is a grouprepresented by the general formula (16) below, wherein R² and p areequivalent to those in the above-noted general formula (8).

[Chemical Formula 8]

Furthermore, in the general formula (7), n indicates a degree ofpolymerization ranging, for example, from 2 to 5000 and preferably from5 to 500. The polymerization may be composed of repeating units with thesame structure or those with different structures. In the latter case,the polymerization form of the repeating units may be a blockpolymerization or a random polymerization.

Moreover, it is preferable that an end on a p-tetrafluorobenzoylenegroup side of the polyaryletherketone represented by the general formula(7) is fluorine and an end on an oxyalkylene group side thereof is ahydrogen atom. Such a polyaryletherketone can be represented by thegeneral formula (17) below, for example. In the general formula (17)below, n indicates a degree of polymerization as in the general formula(7).

[Chemical Formula 9]

Specific examples of the polyaryletherketone represented by the generalformula (7) may include those represented by the general formulae (18)to (21) below, wherein n indicates a degree of polymerization as in thegeneral formula (7).

[Chemical Formula 10]

Other than the above, the polyamide or polyester may be, for example,polyamide or polyester described by JP 10(1998)-508048 A, and theirrepeating units can be represented by the general formula (22) below.

[Chemical Formula 11]

In the above general formula (22), Y is an O atom or an NH group. E is,for example, at least one group selected from the group consisting of acovalent bond, a C₂ alkylene group, a halogenated C₂ alkylene group, aCH₂ group, a C(CX₃)₂ group (wherein X is a halogen atom or a hydrogenatom), a CO group, an O atom, an S atom, an SO₂ group, an Si(R)₂ group,and an N(R) group, and Es may be the same or different. In theabove-mentioned E, R is at least one of a C₁₋₃ alkyl group and ahalogenated C₁₋₃ alkyl group and present at a meta position or a paraposition with respect to a carbonyl functional group or a Y group.

Further, in the above general formula (22), A and A′ are substituents,and t and z respectively indicate the numbers of substitutions therein.Additionally, p is an integer from 0 to 3, q is an integer from 1 to 3,and r is an integer from 0 to 3.

The above-mentioned A is selected from the group consisting of, forexample, a hydrogen atom, a halogen atom, a C₁₋₃ alkyl group, ahalogenated C₁₋₃ alkyl group, an alkoxy group represented by OR (whereinR is the group defined above), an aryl group, a substituted aryl groupby halogenation or the like, a C₁₋₉ alkoxycarbonyl group, a C₁₋₉alkylcarbonyloxy group, a C₁₋₁₂ aryloxycarbonyl group, a C₁₋₁₂arylcarbonyloxy group and a substituted derivative thereof, a C₁₋₁₂arylcarbamoyl group, and a C₁₋₁₂ arylcarbonylamino group and asubstituted derivative thereof When there are plural As, they may be thesame or different. The above-mentioned A is selected from the groupconsisting of, for example, halogen, a C₁₋₃ alkyl group, a halogenatedC₁₋₃ alkyl group, a phenyl group, and a substituted phenyl group andwhen there are plural As, they may be the same or different. Asubstituent on a phenyl ring of the substituted phenyl group can be, forexample, a halogen atom, a C₁₋₃ alkyl group, a halogenated C₁₋₃ alkylgroup, or a combination thereof The t is an integer from 0 to 4, and thez is an integer from 0 to 3.

Among the repeating units of the polyamide or polyester represented bythe general formula (22) above, the repeating unit represented by thegeneral formula (23) below is preferable.

[Chemical Formula 12]

In the general formula (23), A, A′, and Y are those defined by thegeneral formula (22), and v is an integer from 0 to 3, preferably is aninteger from 0 to 2. Although each of x and y is 0 or 1, not both ofthem are 0.

Note here that, among the above-described examples of a polymerexhibiting positive birefringence, a polyester resin is preferable as apolymer exhibiting positive birefringence for forming the birefringentA-layer.

Furthermore, in a mixture of a polymer exhibiting negative birefringenceand a polymer exhibiting positive birefringence used for forming thebirefringent A-layer, a mixing ratio of these polymers can be determinedsuitably so as to obtain the birefringent A-layer with a propertysatisfying ny_(a)≧nz_(a)>nx_(a) or nz_(a)>ny_(a)≧nx_(a).

Preferably, the polymer exhibiting negative birefringence and thepolymer exhibiting positive birefringence contained in the mixture forforming the birefringent A-layer are compatible with each other.Examples of the combination of the polymer exhibiting negativebirefringence and the polymer exhibiting positive birefringence includecombinations of: polymethyl methacrylate and polyethylene oxide;polystyrene and polyphenylene ether; a styrene-maleimide copolymer andpolyphenylene ether; an olefin-maleimide copolymer and anacrylonitrile-styrene copolymer; a styrene-maleic anhydride copolymerand polycarbonate; and polystyrene and polycarbonate.

Note here that anyone having an ordinary skill in the art can preparethe birefringent A-layer with a property satisfying ny_(a)≧nz_(a)>nx_(a)or nz_(a)>ny_(a)≧nx_(a) by, for example, selecting a suitable type ofpolymer out of the above-described various polymers and setting the filmproducing conditions such as stretching or shrinking suitably, withoutconducting any undue experimentation.

Next, in the present invention, it is necessary that the birefringentB-layer has a property satisfying nx_(b)≧ny_(b)>nz_(b). The reason forthis is that the birefringent B-layer with such a property is suitablefor optical compensation of liquid crystal molecules that are in tiltalignment, bend alignment, hybrid alignment, homeotropic alignment orthe like in a liquid crystal cell.

The birefringent B-layer with such a property preferably is formed ofa-polymer exhibiting positive birefringence. Among the above-describedvarious polymers exhibiting positive birefringence, polyimide is morepreferable for forming the birefringent B-layer, because it exhibitshigh birefringence.

It is preferable that the birefiingent B-layer meets the requirementrepresented by the formula (1) below, because this allows excellentcompensation of the black display to be achieved in a VA mode or an OCBmode liquid crystal cell, for example.0.005≦Δn_(b)≦0.2  (1)

In the above formula (1), Δn_(b) is as defined above. It is morepreferable that the birefringent B-layer satisfies 0.01≦Δn_(b)≦0.15,still more preferably 0.015≦Δn_(b)≦0.1.

Note here that anyone having an ordinary skill in the art can preparethe birefringent B-layer with a property satisfying nx_(b)≧ny_(b)>nz_(b)by, for example, selecting a suitable type of polymer out of theabove-described various polymers and setting the film producingconditions such as stretching or shrinking suitably, without conductingany undue experimentation.

The birefringent optical film of the present invention includes at leastone birefringent A-layer and at least one birefringent B-layer. Becausethe birefringent optical film configured as such has a broad range ofΔnd values as well as large Rth values, it allows a liquid crystaldisplay or the like to achieve a wide viewing angle and excellentcontrast when incorporated therein.

In the present invention, the thickness of the birefringent A-layer isnot particularly limited, but may be, for example, 1 to 500 μm,preferably 1 to 300 μm, and more preferably 1 to 200 μm.

Also, the thickness of the birefringent B-layer is not particularlylimited, but may be, for example, 0.1 to 30 μm, preferably 0.3 to 25 μm,and more preferably 0.5 to 20 μm.

The birefringent A-layer may be laminated on one or both surfaces of thebirefringent B-layer, for example. The number of the birefringentA-layers may be one or at least two for each surface. Moreover, thebirefringent A-layer may be laminated directly on the birefringentB-layer, or alternatively, an additional layer(s) may be providedbetween the birefringent A-layer and the birefringent B-layer. The sameapplies to the birefringent B-layer.

Furthermore, the birefringent optical film of the present inventionpreferably meets a requirement represented by the formula (4) below, forexample. The birefringent optical film of the present invention meetingsuch a requirement does not deteriorate the front contrast of a liquidcrystal display or the like when it is provided therein.−3°≦alignment axis accuracy≦3°  (4)

The alignment axis accuracy is as defined above.

It is more preferable that the birefringent optical film satisfies−2°≦alignment axis accuracy≦2°, still more preferably −1.5°≦alignmentaxis accuracy≦1.5°. In particular, when the birefringent optical film isused in a VA mode liquid crystal cell, it is preferable that thebirefringent optical film satisfies −2°≦alignment axis accuracy≦2°. Inthe present invention, it is preferable to shrink or stretch thelaminate of the birefringent A-layer and the birefringent B-layer,because this reduces variation in axis accuracy.

Moreover, the birefringent optical film of the present inventionpreferably has reciprocal wavelength dispersion characteristics. Whenthe birefringent optical film of the present invention has reciprocalwavelength dispersion characteristics, the occurrence of displaycoloring in a liquid crystal display or the like when the birefringentoptical film is incorporated therein can further be prevented. Note herethat the reciprocal wavelength dispersion characteristics show atendency that the in-plane retardation value (Δnd) increases as thewavelength becomes longer. The birefringent optical film of the presentinvention with reciprocal wavelength dispersion characteristics can beused as a reciprocal dispersion film.

Preferably, the birefringent optical film meets the requirementsrepresented by the following formulae (5) and (6), for example. This isbecause, when the birefringent optical film meets the requirementsrepresented by the formulae (5) and (6), the birefringent optical filmhas reciprocal wavelength dispersion characteristics. More specifically,in the present invention, the birefringent A-layer and the bireflingentB-layer are arranged so that their slow axes are orthogonal to eachother, so that the in-plane retardation Δnd of the optical film as awhole corresponds to a difference between the in-plane retardationΔnd_(a) of the birefringent A-layer and the in-plane retardationΔnd_(b)of the birefringent B-layer (Δnd=|Δnd_(a)−Δnd_(b)|). Furthermore,as shown in the graph of FIG. 1, the change A in wavelength dispersioncharacteristics of the absolute value of the in-plane retardationΔnd_(a) of the birefringent A-layer is smaller than the change B in thesame of the birefringent B-layer. Therefore, as shown in the graph ofFIG. 2, the wavelength dispersion characteristics of the optical film ofthe present invention corresponds to the difference between the in-planeretardation of the birefringent A-layer and that of the birefringentB-layer. As a result, the optical film of the present invention hasreciprocal wavelength dispersion characteristics. It is to be noted herethat the graphs of FIGS. 1 and 2 are intended merely to explainwavelength dispersion characteristics, and the present invention is byno means limited to these graphs.|Δnd_(a)|>|Δnd_(b)|  5)α_(a)≦α_(b)  (6)

In the formulae (5) and (6), Δnd_(a), Δnd_(b), α_(a) and α_(b) are asdefined above.

It is possible to allow the birefringent optical film of the presentinvention to meet the requirements represented by the formula (5) and(6) by, for example, selecting the types of materials for forming thebirefringent A-layer and the birefringent B-layer. For example, whenpolyimide is selected as a material for forming the birefringentB-layer, the resultant birefringent B-layer will have significantwavelength dispersion. More specifically, Δnd of the birefringentB-layer becomes greater at a shorter wavelength and smaller at a longerwavelength. As a result, regardless of the type of the material forforming birefringent A-layer, Δnd of the laminate of these layersexhibits reciprocal wavelength dispersion characteristics.

The birefringent optical film of the present invention can be producedby, for example, providing a birefringent A-layer and then forming abirefringent B-layer on the birefringent A-layer.

First, the birefringent A-layer is provided.

The birefringent A-layer is formed, for example, using a polymerexhibiting negative birefringence, a polymer exhibiting positivebirefringence, or a mixture of a polymer exhibiting negativebirefringence and a polymer exhibiting positive birefringence. Thepolymers are as described above.

For example, the birefringent A-layer can be formed using a polymerexhibiting negative birefringence, a polymer exhibiting positivebirefringence, or a mixture of a polymer exhibiting negativebirefringence and a polymer exhibiting positive birefringence accordingto a conventionally known method such as extrusion, a calender method, asolvent casting method or film flow-expanding.

Hereinafter, a method of forming the birefringent A-layer by filmflow-expanding will be described as an example.

For example, a solution or melt of a polymer for forming thebirefringent A-layer is coated on a suitable base and then is hardenedby suitable means (such as heating or cooling). Thereafter, the materialthus hardened is peeled off from the base, thus obtaining a film. Thereis no particular limitation to the base, and an inorganic compound base(an SUS belt, a copper sheet, a glass sheet, an Si wafer or the like), apolymer film, a metal sheet or the like can be used.

Specifically, a material for forming a polymer film serving as the basemay be, for example, a polyolefin (polyethylene, polypropylene or thelike), amorphous polyolefin, polyimide, polyamide imide, polyamide,polyetherimide, polyether ether ketone, polyetherketone, polyketonesulfide, polyether sulfone, polysulfone, polyphenylene sulfide,polyphenylene oxide, polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, polyacetal, polycarbonate,polyarylate, polymethyl methacrylate, polymethacrylate, polyacrylate,polystyrene, polypropylene, a cellulose-based polymer(triacetylcellulose (TAC) or the like), an epoxy resin, a phenol resin,a norbornen-based resin, a polyester resin, a polyether-sulfone resin, apolysulfone resin, a polycarbonate resin, a polyamide resin, a polyimideresin, a polyolefin resin, an acrylic resin, a polynorbornene resin, apolyarylate resin, a polystyrene resin, a polyvinyl alcohol resin, apolyvinyl chloride resin, a polyvinylidene chloride resin, a polyacrylicresin, a mixture of these materials or the like.

Furthermore, other than the above, a liquid crystal polymer or the likealso can be used as a material for forming the base. Moreover, forexample, a mixture formed of a thermoplastic resin whose side chain hasa substituted or unsubstituted imido group and a thermoplastic resinwhose side chain has a substituted or unsubstituted phenyl group and anitrile group, which is described in JP 2001-343529 A (WO 01/37007) alsocan be used. Specific examples thereof include a mixture of analternating copolymer of isobutene and N-methyl maleimide and anacrylonitrile-styrene copolymer.

Among these materials for forming the base, for example, polyethylene,polypropylene, polyethylene terephthalate, polyethylene naphthalate,polymethyl methacrylate, polycarbonate, polyarylate, cellulose-basedpolymers, polyether sulfone, norbornen-based resins, a mixture of analternating copolymer of isobutene and N-methyl maleimide and anacrylonitrile-styrene copolymer, a mixture formed of a thermoplasticresin whose side chain has a substituted or unsubstituted imido groupand a thermoplastic resin whose side chain has a substituted orunsubstituted phenyl group and a nitrile group are preferable. Thepolymer film can be produced using any of the above-mentioned resins byextrusion, a calender method, a solvent casting method or the like.Moreover, the polymer film also may be stretched (uniaxially, biaxially,or the like), and a stretched polymer film is preferable. As the polymerfilm, a polymer film that has been subjected to a surface treatment suchas, for example, a treatment for imparting hydrophilicity, a treatmentfor imparting hydrophobicity, or a treatment for reducing the solubilityof the base also may be used. The thickness of the polymer film isgenerally not less than 10 μm and not more than 200 μm, preferably notless than 20 μm and not less than 150 μm, and particularly preferablynot less than 30 μm and not more than 100 μm.

There is no particular limit to a concentration of a polymer in thepolymer solution for forming the birefrin gent A-layer. For example, inorder to obtain the viscosity facilitating coating, with respect to 100parts by weight of a solvent, the content of the polymer is, forexample, 0.5 to 50 parts by weight, preferably 1 to 40 parts by weight,and more preferably 2 to 30 parts by weight. With respect to 100 partsby weight of a solvent, the content of the polymer preferably is notless than 0.5 parts by weight because this can provide the viscosityappropriate for coating. Further, the content of the polymer preferablyis not more than 50 parts by weight because this can provide theviscosity that allows a smooth coated surface to be formed.

The solvent for the polymer solution for forming the birefringentA-layer is not particularly limited as long as it can dissolve thepolymer, and can be determined suitably according to a type of thepolymer. Specific examples thereof include halogenated hydrocarbons suchas chloroform, dichloromethane, carbon tetrachloride, dichloroethane,tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzeneand orthodichlorobenzene; phenols such as phenol and parachlorophenol;aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzeneand 1,2-dimethoxybenzene; ketone-based solvents such as acetone, methylethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone,2-pyrrolidone and N-methyl-2-pyrrolidone; ester-based solvents such asethyl acetate and butyl acetate; alcohol-based solvents such as t-butylalcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycolmonomethyl ether, diethylene glycol dimethyl ether, propylene glycol,dipropylene glycol and 2-methyl-2,4-pentanediol; amide-based solventssuch as dimethylformamide and dimethylacetamide; nitrile-based solventssuch as acetonitrile and butyronitrile; ether-based solvents such asdiethyl ether, dibutyl ether and tetrahydrofuran; or carbon disulfide,ethyl cellosolve or butyl cellosolve. These solvents may be used aloneor in combination of two or more. Further, preferably, the solvent is ofa type that does not corrode the base.

In the polymer solution for forming the birefringent A-layer, forexample, various additives such as a stabilizer, a plasticizer, metal, acompatibilizer, and the like further may be blended as necessary.

When the above-described additives are blended in the polymer solutionfor forming the birefringent A-layer, the blend amount ranges, forexample, from 0 wt % to 50 wt %, preferably from 0 wt % to 30 wt %, withrespect to the polymer.

Moreover, the polymer solution for forming the birefringent A-layer maycontain other resins. Examples of other resins include resins forgeneral purpose use, engineering plastics, thermoplastic resins andthermosetting resins.

The resins for general purpose use can be, for example, polyethylene(PE), polypropylene (PP), polystyrene (PS), polymethyl methacrylate(PMMA), an ABS resin, an AS resin or the like. The engineering plasticscan be, for example, polyacetate (POM), polycarbonate (PC), polyamide(PA: nylon), polyethylene terephthalate (PET), polybutyleneterephthalate (PBT) or the like. The thermoplastic resins can be, forexample, polyphenylene sulfide (PPS), polyethersulfone (PES), polyketone(PK), polyimide (PI), polycyclohexanedimethanol terephthalate (PCT),polyarylate (PAR), liquid crystal polymers (LCP) or the like. Thethermosetting resins can be, for example, epoxy resins, phenolic novolacresins or the like.

When the above-described other resins or the like are blended in thepolymer solution for forming the birefringent A-layer as mentionedabove, the blend amount ranges, for example, from 0 wt % to 50 wt %,preferably from 0 wt % to 30 wt %, with respect to the polymer.

The coating of polymer solution for forming the birefringent A-layer canbe carried out by a suitable method such as spin coating, rollercoating, flow coating, die coating, blade coating, printing, dipcoating, film flow-expanding, bar coating, gravure printing or the like.In the coating, polymer layers can be superimposed as required.

There is no particular limitation to the polymer melt for forming thebirefringent A-layer. Examples of the melt include a melt in which apolymer as described above is melted by heating. The polymer melt forforming the birefringent A-layer further may contain, for example,various additives such as the above-mentioned stabilizer, plasticizer,metal and the like and other resins as required.

Then, the coating layer of the polymer for forming the birefringentA-layer on the base is hardened, thereby forming a layer on one surfaceof the base.

The hardening method is not particularly limited as long as it allowsthe polymer for forming the birefringent A-layer to be hardened so as toform the layer. Examples of the method include air-drying and drying byheating. The conditions under which the hardening is carried out alsocan be determined suitably according to, for example, the type of thepolymer for forming the birefringent A-layer, and in the case of using asolution, the type of the solvent. For example, a temperature at whichthe hardening is carried out is generally from 40° C. to 250° C.,preferably from 50° C. to 200° C. The hardening may be carried out at aconstant temperature or a temperature raised or lowered in a step-wisemanner. Ahardening time also is not particularly limited. In the case ofusing a polymer solution for forming the birefringent A-layer, it isnecessary to employ a condition that allows a solvent to be removed byhardening. The hardening time is, generally 10 seconds to 60 minutes,and preferably 30 seconds to 30 minutes.

The thickness of the layer formed on the base is not particularlylimited, but may be, for example, 0.2 to 100 μm, preferably 0.5 to 50μm, and more preferably 1 to 20 μm.

In the above-described manner, the birefringent A-layer can be formed onthe base. This birefringent A-layer is peeled off from the base and isused as a film in the following steps. However, depending on the type ofthe base, it is not necessary to peel off the birefringent A-layer fromthe base, and the birefringent A-layer integrated with the base may beused in the following steps.

Examples of the method of peeling off the film layer from the baseinclude: mechanically peeling off the film layer using a roller or thelike; immersing the laminate in a poor solvent for all the materialsforming the laminate and then mechanically peeling off the film layer;peeling off the film layer by applying ultrasonic waves to the laminatein the poor solvent; and subjecting the laminate to temperature change,thereby causing the film layer to be peeled off due to the difference inthermal expansion coefficient between the base and the film layer. Thepeelability of the film layer from the base varies depending on amaterial used for forming the film layer and adhesion between the filmlayer and the base. Thus, the most suitable peeling method may beemployed as appropriate.

Next, a birefringent B-layer is disposed on the birefringent A-layer toobtain a birefringent optical film of the present invention.

For example, a solution or melt of a polymer exhibiting positivebirefringence, for example, is coated on the birefringent A-layer and ishardened, thereby forming a birefringent B-layer on the birefringentA-layer. Thus, the birefringent optical film of the present inventioncan be obtained. When the birefringent A-layer includes a polymerexhibiting positive birefringence, a polymer exhibiting positivebirefringence used for forming the birefringent B-layer may be the sameas or different from the polymer used for forming the birefringentA-layer.

Note here that, with regard to the formation of the birefringentB-layer, the concentration of a polymer in a polymer solution forforming the birefringent B-layer, a solvent of a polymer solution forforming the birefringent B-layer, additives and other resins that mayoptionally be contained in a solution or melt of a polymer for formingthe birefringent B-layer, the blend ratio of additives and other resinswith respect to a polymer for forming the birefringent B-layer, themethod of coating a polymer solution for forming the birefringentB-layer, the method of coating a polymer melt for forming thebirefringent B-layer, and the method and conditions for hardening asolution or melt of a polymer for forming the birefringent B-layer arethe same as those described with regard to the birefringent A-layer.

Also, the birefringent B-layer can be formed separately by, for example,coating a solution or melt of a polymer exhibiting positivebirefringence on a suitable base, hardening the solution or melt byheating or cooling, and then peeling off the hardened material from thebase. The birefringent B-layer formed separately in the above-describedmanner may be bonded to the birefringent A-layer with an adhesive or apressure sensitive adhesive, thereby forming a birefringent optical filmof the present invention including the birefringent A-layer and thebirefringent B-layer.

The adhesive or the pressure sensitive adhesive used for bonding thebirefringent A-layer and the birefringent B-layer is not particularlylimited, but preferably is one having excellent optical transparency andappropriate sticking characteristics such as wettability, cohesiveness,and adhesiveness. The adhesive can be, for example, a polymer adhesivebased on acrylic substances, vinyl alcohol, silicone, polyester,polyurethane or polyether, or a rubber-based adhesive. It also ispossible to use an adhesive containing a water-soluble cross-linkingagent of vinyl alcohol-based polymers such as boric acid, borax,glutaraldehyde, melamine and oxalic acid.

Examples of the pressure-sensitive adhesive include those preparedappropriately based on polymers such as an acrylic polymer, asilicone-based polymer, polyester, polyurethane, polyether, andsynthetic rubber.

Also, the birefringent optical film of the present invention can beproduced by, for example, preparing a precursor layer of thebirefringent A-layer, forming a precursor layer of the birefringentB-layer thereon, and then stretching or shrinking the thus-obtainedlaminate.

The precursor layer of the birefringent A-layer can be formed of thesame material and with the same forming method as those of thebirefringent A-layer described above. Also, the precursor layer of thebirefringent B-layer can be formed of the same material and with thesame forming method as those of the birefringent B-layer describedabove. The only difference between the birefringent A-layer and theprecursor layer thereof is that the birefringent A-layer has, forexample, a property satisfying ny_(a)≧nz_(a)>nx_(a) ornz_(a)>ny_(a)≧nx_(a), whereas the precursor layer thereof does not havesuch a property. In such a case, the birefringent A-layer may be formedby stretching or shrinking the precursor layer of the birefringentA-layer so that the property of the precursor layer is changed to adesired property. Also, the precursor layer of the birefringent B-layerdiffer from the birefringent B-layer only in that it does not have aproperty satisfying nx_(b)>ny_(b)>nz_(b). Thus, as described above, itis possible to form the birefringent B-layer by stretching or shrinkingthe precursor layer of the birefringent B-layer so as to obtain adesired property.

The stretching method is not particularly limited, and may be uniaxialstretching or biaxial stretching. Also, the stretching direction may beeither a film MD direction or a film TD direction of the laminate. Thespecific stretching method also is not particularly limited, and anyknown methods can be used as appropriate. Examples of the stretchingmethod include stretching along the machine direction according tomethods using rollers, tenter transverse stretching, freend longitudinalstretching in which the laminate is stretched uniaxially in the MDdirection, fixed-end transverse stretching in which the laminate isstretched uniaxially in the TD direction with the MD direction beingfixed, simultaneous biaxial stretching in which the laminate isstretched in the TD direction while being shrunk in the MD direction,biaxial stretching in which the laminate is stretched in the MDdirection and then further is stretched in the TD direction.

When the laminate is stretched in the MD direction with the TD directionbeing fixed, molecular alignment in the film in-plane direction can becontrolled more easily. Thus, it is possible to obtain a stretched filmthat exhibits small Δnd values.

Furthermore, when the laminate is stretched in the TD direction with theMD direction being fixed by, for example, fixed-end transversestretching, it is possible to obtain a stretched film that exhibitssmall Δnd values. Moreover, when the laminate that has been stretched inthe TD direction then is shrunk in the direction opposite to the TDdirection, it is possible to obtain a stretched film that exhibitsimproved Δnd, Rth and alignment axis accuracy.

Furthermore, when the laminate is stretched in the TD direction whilebeing shrunk in the MD direction, it is possible to obtain a stretchedfilm that exhibits larger Δnd values and still more improved alignmentaxis accuracy than those of the stretched film obtained by fixed-endtransverse stretching.

Furthermore, when the laminate is stretched in the TD direction, theresultant birefringent optical film can be bonded to a polarizing plateor a polarizer easily so that the longer sides of the birefringentoptical film and the polarizing plate or polarizer overlap each other,whereby an elliptically polarizing plate in which the direction of themaximum refractive index within a plane of the birefringent optical filmis orthogonal to the absorption axis of the polarizing plate isobtained. Accordingly, a so-called “roll-to-roll” production becomespossible, thereby improving the efficiency in production.

Though the stretch ratio of the laminate varies depending on thestretching method, it is in general from 0% to 100% with respect to thelength of the unstretched laminate. Preferably, the stretch ratio of thelaminate is 0% to 70% with respect to the length of the unstretchedlaminate.

The temperature for stretching the laminate is selected suitablydepending on the glass transition point (Tg) of the laminate in use, thekinds of additives in the laminate, and the like. The temperature forstretching the laminate is, for example, 40° C. to 250° C., preferably80° C. to 200° C., and particularly preferably 100° C. to 200° C. It isparticularly preferable that the temperature for stretching the laminateis substantially equal to or higher than Tg of the laminate to bestretched.

The method of shrinking the laminate is not particularly limited, andordinary methods can be applied. The examples include a method in whicha precursor layer of the birefringent A-layer is formed on a base, andthe resultant laminate is heated or cooled so that the base is shrunk,thereby shrinking the laminate as a whole. As the base, a shrinkablebase such as a heat shrinkable film or the like can be used. When usinga shrinkable base, it is preferable to control the shrinkage of the baseusing a stretching machine. Specifically, this can be carried out, forexample, by setting a tenter stretching machine so that the stretchratio of the film would be less than 1 or by setting a longitudinaluniaxial stretching machine so that the stretch ratio of the film wouldbe 1 to cause shrinkage in the width direction.

The heat-shrinkable film can be a film formed of, for example,polyester, polystyrene, polyethylene, polypropylene, polyvinyl chloride,or polyvinylidene chloride.

Furthermore, in the method for producing the birefringent optical filmof the present invention, when preparing the birefringent A-/B-layer,the birefringent A-/B-layer may be formed by providing a precursor layerof the birefringent A-/B-layer and then stretching or shrinking theprecursor layer in the manner described above. In particular, it ispreferable that the birefringent A-/B-layer is formed by stretching aprecursor layer of the birefringent A-/B-layer that is formed of apolymer exhibiting positive birefringence. Furthermore, when thebirefiingent optical film includes, for example, three birefiingentA-layers, the birefringent A-layers can be formed in the followingmanner. First, three precursor layers for forming these threebirefringent A-layers are provided and laminated with each other.Adhesive layers are formed between the respective precursor layers. Bystretching or shrinking the three precursor layers altogether in theabove-described manner, the birefringent A-layers as the laminate withthree-layer structure can be formed.

Furthermore, as described above, the birefringent optical film of thepresent invention preferably meets the requirement represented by thefollowing formula (4). This is because the birefringent optical film ofthe present invention meeting this requirement is practical whenincorporated in a liquid crystal display or the like.−3°≦alignment axis accuracy≦3°  (4)

Note here that the alignment axis accuracy is as defined above.

Still further, the birefringent optical film of the present inventionpreferably meets the requirements represented by the following formulae(5) and (6). This is because, when the birefringent optical film meetsthe requirements represented by the formulae (5) and (6), thebirefringent optical film has reciprocal wavelength dispersioncharacteristics so that display coloring can further be prevented asdescribed above.|Δnd_(a)|>|Δnd_(b)|  5)α_(a)≦α_(b)  (6)

Note here that Δnd_(a), Δnd_(b), α_(a) and α_(b) are as defined above.

The birefringent optical film according to the present invention may beused alone or, if required, in combination with an additional opticalfilm or the like to form a laminate for various optical uses, e.g.,optical compensating members of various liquid crystal display elements.For example, the birefiingent optical film of the present invention maybe used in combination with an iodine-based or dyestuff-based polarizingplate (or polarizer) produced industrially, so as to provide a laminatedpolarizing plate having a function of compensating and adjusting thebirefiingence of a liquid crystal display element.

The polarizing plate that may optionally be used in combination with thebirefringent optical film according to the present invention is notparticularly limited. However, the polarizing plate basically isconfigured by laminating a protective layer (film) on at least onesurface of a polarizer.

The polarizer (polarizing film) is not particularly limited, but can bea film prepared by a conventionally known method of, for example, dyeingby allowing a film of various kinds to adsorb a dichroic material suchas iodine or a dichroic dye, followed by crosslinking, stretching, anddrying. Especially, films that transmit linearly polarized light whennatural light is made to enter those films are preferable, and filmshaving excellent light transmittance and polarization degree arepreferable. Examples of the film of various kinds in which the dichroicmaterial is to be adsorbed include hydrophilic polymer films such aspolyvinyl alcohol (PVA)-based films, partially-formalized PVA-basedfilms, partially-saponified films based on ethylene-vinyl acetatecopolymer, and cellulose-based films. Other than the above, polyenealigned films such as dehydrated PVA and dehydrochlorinated polyvinylchloride can be used, for example. Among them, a PVA-based film preparedby adsorbing iodine or a dichroic dye and aligning the film is usedpreferably. The thickness of the polarizing film generally is in therange from 1 to 80 μm, though it is not limited to this.

The protective layer (film) is not particularly limited, but can be aconventionally known transparent film. For example, transparentprotective films having excellent transparency, mechanical strength,thermal stability, moisture shielding property, and isotropism arepreferable. Specific examples of materials for such a transparentprotective layer include cellulose-based resins such astriacetylcellulose; transparent resins based on polyester,polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone,polystyrene, polynorbornene, polyolefin, acrylic substances, acetate,and the like; mixtures of a thermoplastic resin whose side chain has asubstituted or unsubtituted imido group and a thermoplastic resin whoseside chain has a substituted or unsubtituted phenyl group and nitrilegroup; and liquid crystal polymers. Thermosetting resins orultraviolet-curing resins based on the acrylic substances, urethane,acrylic urethane, epoxy, silicones, and the like can be used as well.Among them, a TAC film having a surface saponified with alkali or thelike is preferable in light of the polarization property and durability.

Moreover, as the protective layer, the polymer film described in JP2001-343529 A (WO 01/37007) also can be used. The polymer material usedcan be a resin composition containing a thermoplastic resin whose sidechain has a substituted or unsubtituted imido group and a thermoplasticresin whose side chain has a substituted or unsubtituted phenyl groupand nitrile group, for example, a resin composition containing analternating copolymer of isobutene and N-methyl maleimide and anacrylonitrile-styrene copolymer. Alternatively, the polymer film may beformed by extruding the resin composition.

It is preferable that the protective layer is colorless, for example.More specifically, a retardation value (Rth) of the film in itsthickness direction as represented by the equation below preferablyranges from −90 nm to +75 nm, more preferably ranges from −80 nm to +60nm, and particularly preferably ranges from −70 nm to +45 nm. When theretardation value is within the range of −90 nm to +75 nm, coloring(optical coloring) of the polarizing plate, which is caused by theprotective film, can be solved sufficiently. In the equation below, nx,ny, and nz are the same as those described above, and d represents athickness of the protective film.Rz{[(nx+ny)/2]−nz}·d

The transparent protective layer further may have an opticallycompensating function. As such a transparent protective layer having theoptically compensating function, it is possible to use, for example, aknown layer used for preventing coloring caused by changes in a visibleangle based on retardation in a liquid crystal cell or for widening apreferable viewing angle. Specific examples include various stretchedfilms obtained by stretching the above-described transparent resinsuniaxially or biaxially, an alignment film of a liquid crystal polymeror the like, and a laminate obtained by providing an alignment layer ofa liquid crystal polymer or the like on a transparent base. Among theabove, the alignment film of a liquid crystal polymer is preferablebecause a wide viewing angle with excellent visibility can be achieved.Particularly preferable is an optically compensating retardation plateobtained by supporting an optically compensating layer with theabove-mentioned triacetylcellulose film or the like, where the opticallycompensating layer is made of an incline-alignment layer of a discoticor nematic liquid crystal polymer. This optically compensatingretardation plate can be a commercially available product, for example,“WV film” manufactured by Fuji Photo Film Co., Ltd. Alternatively, theoptically compensating retardation plate can be prepared by laminatingtwo or more layers of the retardation film and the film support oftriacetylcellulose film or the like so as to control the opticalcharacteristics such as retardation.

The thickness of the transparent protective layer is not particularlylimited and can be determined suitably according to retardation or aprotective strength, for example. The thickness of the transparentprotective layer is, for example, not more than 500 μm, preferably inthe range from 5 μm to 300 μm, and more preferably in the range from 5μm to 150 μm.

The transparent protective layer can be formed suitably by aconventionally known method such as a method of coating a polarizingfilm with the above-mentioned various transparent resins or a method oflaminating the transparent resin film, the optically compensatingretardation plate, or the like on the polarizing film, or can be acommercially available product.

The transparent protective layer further may be subjected to, forexample, a hard coating treatment, an antireflection treatment,treatments for anti-sticking, diffusion and anti-glaring and the like.The hard coating treatment aims to prevent scratches on the surfaces ofthe polarizing plate, and is a treatment of, for example, providing ahardened coating film that is formed of a curable resin and hasexcellent hardness and smoothness on a surface of the transparentprotective layer. The curable resin can be, for example,ultraviolet-curing resins of silicone base, urethane base, acrylic, andepoxy base. The treatment can be carried out by a conventionally knownmethod. The anti-sticking treatment aims to prevent adjacent layers fromsticking to each other. The antireflection treatment aims to preventreflection of external light on the surface of the polarizing plate, andcan be carried out by forming a conventionally known antireflectionlayer or the like.

The anti-glare treatment aims to prevent reflection of external light onthe polarizing plate surface from hindering visibility of lighttransmitted through the polarizing plate. The anti-glare treatment canbe carried out, for example, by providing microscopic asperities on asurface of the transparent protective layer by a conventionally knownmethod. Such microscopic asperities can be provided, for example, byroughening the surface by sand-blasting or embossing, or by blendingtransparent fine particles in the above-described transparent resin whenforming the transparent protective layer.

The above-described transparent fine particles may be silica, alumina,titania, zirconia, stannic oxide, indium oxide, cadmium oxide, antimonyoxide, or the like. Other than the above, inorganic fine particleshaving an electrical conductivity, organic fine particles including, forexample, crosslinked or uncrosslinked polymer particles, or the like canbe used as well. The average particle diameter of the transparent fineparticles ranges, for example, from 0.5 to 20 m, though there is noparticular limitation. A blend ratio of the transparent fine particlesranges, for example, from 2 to 70 parts by weight, preferably from 5 to50 parts by weight with respect to 100 parts by weight of theabove-described transparent resin, though there is no particularlimitation.

An anti-glare layer in which the transparent fine particles are blendedcan be used as the transparent protective layer itself or provided as acoating layer or the like applied onto the transparent protective layersurface. Furthermore, the anti-glare layer also can function as adiffusion layer to diffuse light transmitted through the polarizingplate in order to widen the viewing angle (i.e., visually-compensatingfunction).

The antireflection layer, the anti-sticking layer, the diffusion layer,the anti-glare layer, and the like as mentioned above can be laminatedon the polarizing plate, as a sheet of optical layers including theselayers, separately from the transparent protective layer.

The method of laminating the respective components (the birefringentoptical film, the polarizer, the transparent protective film, etc.) isnot particularly limited but a conventionally known method can beapplied. In general, pressure-sensitive adhesives, adhesives, and thelike as described above can be used, and the kinds thereof can bedetermined suitably depending on the materials or the like of thecomponents. Examples of the adhesives include polymer adhesives based onacrylic substances, vinyl alcohol, silicone, polyester, polyurethane,polyester, or the like and rubber-based adhesives. The above-mentionedpressure-sensitive adhesives and adhesives do not peel off easily evenwhen being exposed to moisture or heat, for example, and have excellentlight transmittance and polarization degree. More specifically, PVAadhesives are preferable when the polarizer is formed of a PVA-basedfilm, in light of stability of adhering treatment. These adhesive andpressure-sensitive adhesive may be applied directly to surfaces of thepolarizing layer and the transparent protective layer, or a layer of atape or a sheet formed of the adhesive or pressure-sensitive adhesivemay be arranged on the surfaces thereof. Further, when these adhesiveand pressure-sensitive adhesive are prepared as an aqueous solution, forexample, other additives or a catalyst such as an acid catalyst may beblended as necessary.

In the case of applying the adhesive, other additives or a catalyst suchas an acid catalyst further may be blended in the aqueous solution ofthe adhesive. Though the thickness of the adhesive layer is notparticularly limited, for example, it is from 1 nm to 500 nm, preferablyfrom 10 nm to 300 nm, and more preferably from 20 nm to 100 nm. It ispossible to adopt a known method of using an adhesive etc. such as anacrylic polymer or a vinyl alcohol-based polymer without any particularlimitations.

The birefringent optical film of the present invention may be used incombination with various retardation plates, diffusion-control films,brightness-enhancement films, and the like. Examples of the retardationplates include those obtained by uniaxially or biaxially stretching apolymer, those subjected to a treatment for causing Z-axis alignment,and those obtained by applying a liquid crystal polymer. Examples of thediffusion-control films include films that control viewing angles byutilizing diffusion, scattering, and refraction and films that controlglaring, scattered light, and the like that affect the resolution byutilizing diffusion, scattering, and refraction. Examples of thebrightness-enhancement films include brightness-enhancement filmsutilizing the selective reflection property of a cholesteric liquidcrystal and provided with a λ/4 plate and scattering films utilizing ananisotropic scatter depending on the polarization direction. Also, theoptical film may be used in combination with a wire grid polarizer.

The laminated polarizing plate of the present invention can be usedsuitably for forming various liquid crystal displays, for example. Whenusing the laminated polarizing plate in a liquid crystal display or thelike, one or more other optical layers such as a reflection plate, asemitransparent reflection plate, and a brightness-enhancement film canbe laminated additionally as required via an adhesive layer or apressure-sensitive adhesive layer.

An example of a reflective polarizing plate or a semitransparentreflective polarizing plate will be described. The reflective polarizingplate is prepared by laminating further a reflection plate on alaminated polarizing plate according to the present invention, and thesemitransparent reflective polarizing plate is prepared by laminating asemitransparent reflection plate on a laminated polarizing plateaccording to the present invention.

In general, the reflective polarizing plate is arranged on a backside ofa liquid crystal cell in order to make a liquid crystal display(reflective liquid crystal display) that reflects incident light from avisible side (display side). The reflective polarizing plate isadvantageous in that, for example, it allows the liquid crystal displayto be thinned further because the necessity of providing a light sourcesuch as a backlight can be eliminated.

The reflective polarizing plate can be formed in any known manner suchas forming a reflection plate of metal or the like on one surface of apolarizing plate having a certain elastic modulus. More specifically,one example thereof is a reflective polarizing plate formed by mattingone surface (surface to be exposed) of a transparent protective layer ofthe polarizing plate as required, and providing the surface with adeposited film or a metal foil formed of a reflective metal such asaluminum.

Another example is a reflective polarizing plate prepared by forming, ona transparent protective layer having a surface with microscopicasperities due to microparticles contained in various transparentresins, a reflection plate corresponding to the microscopic asperities.The reflection plate having a surface with microscopic asperitiesdiffuses incident light irregularly so that directivity and glare can beprevented and irregularity in color tones can be controlled. Thereflection plate can be formed by attaching the metal foil or the metaldeposited film directly on the surface with asperities of thetransparent protective layer by any conventionally known methodsincluding deposition and plating, such as vacuum deposition, ionplating, and sputtering.

As mentioned above, the reflection plate can be formed directly on atransparent protective layer of a polarizing plate. Alternatively, areflecting sheet or the like formed by providing a reflecting layer on aproper film such as the transparent protective film can be used as thereflection plate. Since a typical reflecting layer of a reflection plateis made of a metal, it is preferably used in a state that the reflectingsurface of the reflecting layer is coated with the film, a polarizingplate, or the like, in order to prevent a reduction of the reflectancedue to oxidation, and furthermore, to allow the initial reflectance tobe maintained for a long period and to avoid the necessity of forming atransparent protective layer separately.

On the other hand, the semitransparent polarizing plate is provided byreplacing the reflection plate in the above-mentioned reflectivepolarizing plate by a semitransparent reflection plate. Examples of asemitransparent polarizing plate include a half mirror that reflects andtransmits light at the reflecting layer.

In general, such a semitransparent polarizing plate is arranged on abackside of a liquid crystal cell. In a liquid crystal display includingthe semitransparent polarizing plate, incident light from the visibleside (display side) is reflected to display an image when a liquidcrystal display is used in a relatively bright atmosphere, while in arelatively dark atmosphere, an image is displayed by using a built-inlight source such as a backlight on the backside of the semitransparentpolarizing plate. In other words, the semitransparent polarizing platecan be used to form a liquid crystal display that can save energy for alight source such as a backlight under a bright atmosphere, while abuilt-in light source can be used under a relatively dark atmosphere.

The following description is about an example of a birefringent opticalfilm, a laminated polarizing plate, or the like prepared by furtherlaminating a brightness-enhancement film on the birefringent opticalfilm, the laminated polarizing plate, or the like according to thepresent invention.

A suitable example of the brightness-enhancement film is notparticularly limited, but it can be selected from a multilayer thin filmof a dielectric or a laminate of multiple thin films with variedrefraction aeolotropy that transmits linearly polarized light having apredetermined polarization axis while reflecting other light. Examplesof such a brightness-enhancement film include “D-BEF (trade name)”manufactured by 3M Co. Also, a cholesteric liquid crystal layer, morespecifically, an alignment film of a cholesteric liquid crystal polymeror an alignment liquid crystal layer fixed onto a supportive film basecan be used as a brightness-enhancement film. Such abrightness-enhancement film reflects either clockwise orcounterclockwise circularly polarized light while it transmits otherlight. Examples of such a brightness-enhancement film include “PCF 350(trade name)” manufactured by Nitto Denko Corporation, “Transmax (tradename)” manufactured by Merck and Co., Inc., and the like.

An optical member including a laminate of at least two theabove-mentioned optical layers can be formed, for example, by a methodof laminating layers separately in a certain order in the process formanufacturing a liquid crystal display or the like. However, efficiencyin manufacturing a liquid crystal display or the like can be improved byusing an optical member that has been laminated previously because ofits excellent stability in quality, assembling operability, and thelike. Any appropriate adhesion means such as a pressure-sensitiveadhesive layer can be used for lamination as in the above.

Moreover, it is preferable that the birefringent optical film, thelaminated polarizing plate, or the like according to the presentinvention further has a pressure-sensitive adhesive layer or an adhesivelayer so as to allow easier lamination onto the other members such as aliquid crystal cell. They can be arranged on one surface or bothsurfaces of the birefringent optical film, the laminated polarizingplate, or the like. The material for the pressure-sensitive adhesivelayer is not particularly limited but can be a conventionally knownmaterial such as acrylic polymers. In particular, the pressure-sensitiveadhesive layer having a low moisture absorption coefficient and anexcellent thermal resistance is preferable from the aspects ofprevention of foaming or peeling caused by moisture absorption,prevention of degradation in the optical characteristics and warping ofa liquid crystal cell caused by difference in thermal expansioncoefficients, a capability of forming a liquid crystal display with highquality and excellent durability, and the like. It also may be possibleto incorporate fine particles so as to form the pressure-sensitiveadhesive layer showing light diffusion property. For the purpose offorming the pressure-sensitive adhesive layer on the surface of theoptical film, the laminated polarizing plate, or the like, a solution ormelt of a sticking material can be applied directly on a predeterminedsurface of the optical film, the laminated polarizing plate, or the likeby a development method such as flow-expansion and coating.Alternatively, a pressure-sensitive adhesive layer can be formed on aseparator, which will be described below, in the same manner andtransferred to a predetermined surface of the birefringent optical film,the laminated polarizing plate, or the like.

In the case where a surface of a pressure-sensitive adhesive layer or anadhesive layer provided on the birefringent optical film, the laminatedpolarizing plate, or the like is exposed, it is preferable to cover thesurface with a separator tentatively so as to prevent contaminationuntil the pressure-sensitive adhesive layer or the adhesive layer is putto use. The separator can be made of a suitable film, e.g., theabove-mentioned transparent protective film, coated with a peeling agentif required. The peeling agent may be selected, for example, from asilicone-based agent, a long-chain alkyl-based agent, a fluorine-basedagent, an agent containing molybdenum sulfide, and the like.

The respective layers such as the polarizer, the transparent protectivelayer, the pressure-sensitive adhesive layer, or the adhesive layer forcomposing the birefringent optical film or the laminated polarizingplate according to the present invention may be subjected to a suitabletreatment such as a treatment with an UV absorber, e.g., salicylateester compounds, benzophenone compounds, benzotriazole compounds,cyanoacrylate compounds, or nickel complex salt-based compounds, thusproviding an UV absorbing capability.

The birefringent optical film and the laminated polarizing plateaccording to the present invention can be used preferably for formingvarious devices such as liquid crystal displays. For example, apolarizing plate can be arranged on at least one surface of a liquidcrystal cell so as to be applied to, for example, a reflection-type,semi-transmission-type, or transmission and reflection type liquidcrystal display. A liquid crystal cell to compose the liquid crystaldisplay can be selected arbitrarily. For example, it is possible to useliquid crystal cells of appropriate types such as active matrix drivingtype represented by a thin film transistor type, a simple matrix drivingtype represented by a twist nematic type and a super twist nematic type.

Examples of the liquid crystal cell include STN (Super Twisted Nematic)cells, TN (Twisted Nematic) cells, IPS (In-Plane Switching) cells, VA(Vertical Aligned) cells, OCB (Optically Aligned Birefringence) cells,HAN (Hybrid Aligned Nematic) cells, ASM (Axially Symmetric AlignedMicrocell) cells, ferroelectric cells, and antiferroelectric cells. Thecells may be subjected to an alignment-division systematically orrandomly. The birefringent optical film according to the presentinvention is excellent particularly in optical compensation of VA(Vertical Aligned) cells.

Since the optical film according to the present invention are excellentparticularly in optical compensation of a VA (Vertical Aligned) cell,they are most suitably used for viewing-angle compensating films for VAmode liquid crystal displays.

In general, a typical liquid crystal cell is composed of opposing liquidcrystal cell substrates and a liquid crystal injected into a spacebetween the substrates. The liquid crystal cell substrates can be madeof glass, plastics, or the like without any particular limitations.Materials for the plastic substrates can be selected from conventionallyknown materials without any particular limitations.

When polarizing plates or optical members are arranged on both sides ofa liquid crystal cell, the polarizing plates or the optical members onthe surfaces can be the same or different type. Moreover, for forming aliquid crystal display, one or more layers of appropriate members suchas a prism array sheet, a lens array sheet, an optical diffuser, and abacklight can be arranged at proper positions.

The birefringent optical film and the laminated polarizing plateaccording to the present invention can be used not only in theabove-described liquid crystal displays but also in, for example,self-light-emitting displays such as organic electroluminescence (EL)displays, plasma displays (PD) and field emission displays (FED). Whenthe optical film or the laminated polarizing plate of the presentinvention is used in a self-light-emitting flat display, the opticalfilm or the laminated polarizing plate can be used as an antireflectionfilter because circularly polarized light can be obtained by setting thein-plane retardation value Δnd of the birefringent optical film to λ/4,for example.

The following is a specific description of an electroluminescence (EL)display including a laminated polarizing plate according to the presentinvention. The EL display of the present invention is a display having abirefringent optical film or a laminated polarizing plate according tothe present invention, and can be either an organic EL display or aninorganic EL display.

In recent EL displays, for preventing reflection from an electrode in ablack state, use of an optical film such as a polarizer and a polarizingplate as well as a λ/4 plate is proposed. The laminated polarizing plateand the birefringent optical film according to the present invention areespecially useful when linearly-polarized light, circularly polarizedlight, or elliptically polarized light is emitted from an EL layer. Thepolarizing plate with optical compensation function according to thepresent invention is especially useful even when an oblique light beamis partially polarized even in the case where natural light is emittedin a front direction.

A typical organic EL display will be explained below. In general, suchan organic EL display has a luminant (organic EL luminant) that isprepared by laminating a transparent electrode, an organic luminantlayer, and a metal electrode in this order on a transparent substrate.Here, the organic ruminant layer is a laminate of various organic thinfilms. Examples thereof include various combinations such as a laminateof a hole injection layer made of a triphenylamine derivative or thelike and a luminant layer made of a phosphorous organic solid such asanthracene; a laminate of the luminant layer and an electron injectionlayer made of a perylene derivative or the like; and a laminate of thehole injection layer, the luminant layer, and the electron injectionlayer.

In general, the organic EL display emits light on the followingprinciple: a voltage is applied to the anode and the cathode so as toinject holes and electrons into the organic luminant layer, energygenerated by the re-bonding of these holes and electrons excites thephosphor, and the excited phosphor emits light when it returns to thebasis state. The mechanism of the re-bonding of these holes andelectrons during the process is similar to that of an ordinary diode.This implies that current and the light emitting intensity exhibit aconsiderable nonlinearity accompanied with a rectification with respectto the applied voltage.

It is preferred for the organic EL display that at least one of theelectrodes is transparent so as to obtain luminescence at the organicluminant layer. In general, a transparent electrode of a transparentconductive material such as indium tin oxide (ITO) is used for theanode. Use of substances having small work function for the cathode isimportant for facilitating the electron injection and thereby raisingluminous efficiency, and in general, metal electrodes such as Mg—Ag andAl—Li can be used.

In an organic EL display configured as described above, it is preferablethat the organic ruminant layer is made of a film that is extremely thinsuch as about 10 nm, so that the organic ruminant layer can transmitsubstantially whole light as the transparent electrode does. As aresult, when the layer does not illuminate, a light beam entering fromthe surface of the transparent substrate passes through the transparentelectrode and the organic luminant layer and is reflected at the metalelectrode so that it comes out again to the surface of the transparentsubstrate. Thereby, the display surface of the organic EL display lookslike a mirror when viewed from exterior.

In the organic EL display induding an organic EL luminant having atransparent electrode on the surface side of an organic luminant layerand a metal electrode on the back surface of the organic ruminant layer,for example, it is preferable that a birefringent optical film or alaminated polarizing plate according to the present invention isarranged on the surface of the transparent electrode, and furthermore, aλ/4 plate is arranged between the polarizing plate and an EL element. Asdescribed above, an organic EL display obtained by arranging abirefringent optical film according to the present invention cansuppress external reflection and improve the visibility. It is furtherpreferable that a retardation plate is arranged between the transparentelectrode and the birefringent optical film.

The retardation plate and the birefringent optical film (the polarizingplate or the like) polarize, for example, light which enters fromoutside and is reflected by the metal electrode, and thus thepolarization has an effect that the mirror of the metal electrode cannotbe viewed from exterior. Particularly, the mirror of the metal electrodecan be blocked completely by forming the retardation plate with aquarter wavelength plate and adjusting an angle formed by thepolarization directions of the retardation plate and the polarizingplate to be π/4. That is, the polarizing plate transmits only thelinearly polarized light component among the external light entering theorganic EL display. In general, the linearly polarized light is changedinto elliptically polarized light by the retardation plate. When theretardation plate is a quarter wavelength plate and when the angle isπ/4, the light is changed into circularly polarized light.

This circularly polarized light passes through, for example, thetransparent substrate, the transparent electrode, and the organic thinfilm. After being reflected by the metal electrode, the light passesagain through the organic thin film, the transparent electrode, and thetransparent substrate, and turns into linearly polarized light at theretardation plate. Moreover, since the linearly polarized light crossesthe polarization direction of the polarizing plate at a right angle, itcannot pass through the polarizing plate. Consequently, as describedabove, the mirror of the metal electrode can be blocked completely.

EXAMPLES

Hereinafter, the present invention will be described more specificallyby way of examples and comparative examples. However, the presentinvention is by no means limited to the following examples. Thecharacteristics of optical films were evaluated in the following manner.

The retardation and alignment axis accuracy were measured using aretardation meter (manufactured by Oji Scientific Instruments, tradename: KOBRA 21ADH).

The film thickness was measured using a magnetic spectrophotometer(manufactured by Otsuka Electronics Co., Ltd., trade name: MCPD-2000) atwavelengths of 700 to 900 nm according to optical interferometry.

Δnd, Rth and α of birefringent A-layers, birefringent B-layers andbirefringent optical films obtained in the following examples andcomparative examples were determined by the following equations.Δnd=(nx−ny)·d,Rth=(nx−nz)·d,α=Δnd_(430 nm)/Δnd_(550 nm)

In the above equations, nx, ny, and nz respectively represent refractiveindices in an X-axis direction, a Y-axis direction, and a Z-axisdirection in each of the layers (films), with the X-axis direction beingan axial direction exhibiting a maximum refractive index within a planeof each of the layers (Elms), the Y-axis direction being an axialdirection perpendicular to the X axis within the plane, and the Z-axisdirection being a thickness direction perpendicular to the X axis andthe Y axis.

In the above equations, Δnd_(430 nm) and Δnd_(550 nm) respectivelyrepresent Δnd at a wavelength of 430 nm and Δnd at a wavelength of 550nm.

Example 1

Polyimide represented by a formula (24) below and having aweight-average molecular weight (Mw) of 100,000 was first synthesizedfrom 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and then dissolved inmethyl isobutyl ketone to prepare a 20 wt % solution of this polyimide.

[Chemical Formula 13]

This polyimide solution was applied onto one surface of “Acryplen (tradename)” (120 Rm in thickness) manufactured by Mitsubishi Rayon Co., Ltd.by casting so as to form a 6.2 μm thick layer of the polyimide solutionon the Acryplen, thus obtaining a laminate. After the application of thepolyimide solution, the laminate was dried at 90° C. for 10 minutes.This laminate was then stretched 8% at 100° C. by longitudinal uniaxialstretching, thus obtaining a birefringent optical film as a laminateincluding a birefringent A-layer formed of the Acryplen and abirefringent B-layer formed of a polyimide coating layer. Table 1 showsthe thickness d_(a), Δnd_(a), Rth_(a), α_(a) and optical characteristicsof the thus-obtained birefringent A-layer, the thickness d_(b), Δnd_(b),Rth_(b), Δnxz, α_(b) and optical characteristics of the thus-obtainedbirefringent BSlayer, and the thickness d, Δnd and Rth of thethus-obtained birefringent optical film. Note here that Anxz isrepresented by Δnxz=nx−nz, where nx and nz are as defined above.

Example 2

An acrylonitrile-styrene copolymer resin was dissolved indichloromethane to prepare a 30 wt % solution of this copolymer resin.This solution was applied onto a polyethylene terephthalate film (PET(base)) by casting and allowed to stand at 100° C. for 30 minutes. Thecopolymer resin layer was then peeled off from the PET film. Thus, a 150μm thick film was obtained. The thus-obtained film was then stretched30% at 120° C. by free-end longitudinal stretching, thus obtaining a 132μm thick birefringent A-layer.

On the other hand, polyimide represented by the above formula (24) andhaving a weight-average molecular weight (Mw) of 100,000 was firstsynthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane and2,2′-bis(trifluoromethyl)-4,4′-dianiinobiphenyl and then dissolved inmethyl isobutyl ketone to prepare a 20 wt % solution of this polyimide.

This polyimide solution was applied onto one surface of a TAC film (80μm in thickness) by casting so as to form a 10.8 μm thick layer of thepolyimide solution on the TAC film, thus obtaining a laminate. After theapplication of the polyimide solution, the laminate was dried at 100° C.for 10 minutes. This laminate was then stretched 3% at 150° C. byfixed-end transverse uniaxial stretching. Thereafter, the polyimidelayer was peeled off from the TAC film. Thus, a birefringent B-layer wasobtained.

The birefringent A-layer and the birefringent B-layer were bonded toeach other via an acrylic pressure sensitive adhesive layer (20 μm inthickness) so that the directions exhibiting the maximum refractiveindices in the respective layers were orthogonal to each other, thusobtaining a birefringent optical film. Table 1 shows the thickness da,Δnd_(a), Rth_(a), a. and optical characteristics of the thus-obtainedbirefringent A-layer, the thickness d_(b), Δnd_(b), Rth_(b), Δnxz, α_(b)and optical characteristics of the thus-obtained birefringent B-layer,and the thickness d, Δnd and Rth of the thus-obtained birefringentoptical film.

Example 3

A biaxially stretched polypropylene film (60 μm in thickness) was bondedto each surface of a polycarbonate film via an acrylic pressuresensitive adhesive layer (20 μm in thickness). The thus-obtainedlaminate was stretched 7% at 150° C. by free-end longitudinal uniaxialstretching, thus obtaining a 40 μm thick birefringent A-layer.

On the other hand, polyimide represented by the above formula (24) andhaving a weight-average molecular weight (Mw) of 100,000 was firstsynthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and then dissolved inmethyl isobutyl ketone to prepare a 20 wt % solution of this polyimide.

This polyimide solution was applied onto one surface of a TAC film (80μm in thickness) by casting so as to form a 9.5 μm thick layer of thepolyimide solution on the TAC film, thus obtaining a laminate. After theapplication of the polyimide solution, the laminate was dried at 100° C.for 10 minutes. This laminate was then stretched 7% at 150° C. byfixed-end transverse stretching. Thereafter, the polyimide layer waspeeled off from the TAC film. Thus, a birefringent B-layer was obtained.

The birefringent A-layer and the birefringent B-layer were bonded toeach other via an acrylic pressure sensitive adhesive layer (20 μm inthickness) so that the directions exhibiting the maximum refractiveindices in the respective layers were orthogonal to each other, thusobtaining a birefringent optical film. Table 1 shows the thicknessd_(a), Δnd_(a), Rth_(a), α_(a) and optical characteristics of thethus-obtained birefringent A-layer, the thickness d_(b), Δnd_(b),Rth_(b), Δnxz, α_(b) and optical characteristics of the thus-obtainedbirefringent B-layer, and the thickness d, Δnd and Rth of thethus-obtained birefringent optical film.

Comparative Example 1

Polyimide represented by the above formula (24) and having aweight-average molecular weight (Mw) of 100,000 was first synthesizedfrom 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and then dissolved inmethyl isobutyl ketone to prepare a 15 wt % solution of this polyimide.

This polyimide solution was applied onto one surface of “ZEONOR (tradename)” (100 μm in thickness) manufactured by ZEON Corporation by castingso as to form a 6 μm thick layer of the polyimide solution on theZEONOR, thus obtaining a laminate. After the application of thepolyimide solution, the laminate was dried at 130° C. for 5 minutes. Thelaminate was then stretched 7% at 130° C. by fixed-end transversestretching, thus obtaining a birefringent optical film as a laminateincluding a birefringent A-layer formed of the ZEONOR and a birefringentB-layer formed of a polyimide coating layer. Table 1 shows the thicknessd_(a), Δnd_(a), Rth_(a), α_(a) and optical characteristics of thethus-obtained birefringent A-layer, the thickness d_(b), Δnd_(b),Rth_(b), Δnxz, α_(b) and optical characteristics of the thus-obtainedbirefringent B-layer, and the thickness d, Δnd and Rth of thethus-obtained birefringent optical film.

Comparative Example 2

A film “ARTON (trade name)” (100 μm in thickness) manufactured by JSRCorporation was stretched 20% at 175° C. by fixed-end transversestretching, thus obtaining a birefringent optical film composed only ofa birefringent A-layer. Table 1 shows the thickness d_(a), Δnd_(a),Rth_(a), α_(a) and optical characteristics of the thus-obtainedbirefringent A-layer.

Comparative Example ₃

A film “Acryplen (trade name)” (120 μm in thickness) manufactured byMitsubishi Rayon Co., Ltd. was stretched 60% at 100° C. by free-endlongitudinal stretching, thus obtaining a birefringent optical filmcomposed only of a birefringent A-layer. Table 1 shows the thicknessd_(a), Δnd_(a), Rth_(a), a. and optical characteristics of thethus-obtained birefringent A-layer.

Comparative Example 4

Polyimide represented by the above formula (24) and having aweight-average molecular weight (Mw) of 100,000 was first synthesizedfrom 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and then dissolved inmethyl isobutyl ketone to prepare a 15 wt % solution of this polyimide.

This polyimide solution was applied onto one surface of a TAC film (as abase) by casting so as to form a 6.5 μm thick layer of the polyimidesolution on the TAC film, followed by drying at 100° C. for 10 minutes.Then, the base and the polyamide coating layer altogether were stretched10% at 150° C. by fixed-end transverse stretching. Thereafter, thepolyamide coating layer was peeled off from the TAC film (the base),thereby obtaining a birefringent optical film composed only of abirefringent B-layer. Table 1 shows the thickness d_(b), Δnd_(b),Rth_(b), Δnxz, α_(b) and optical characteristics of the thus-obtainedbirefringent B-layer. TABLE 1 Birefringent optical A-layer B-layer filmd_(a) Δnd_(a) Rth_(a) d_(b) Δnd_(b) Rth_(b) d Δnd Rth (μm) (nm) (nm)α_(a) (μm) (nm) (nm) Δnxz α_(b) (μm) (nm) (nm) Ex. 1 119 −15 −14 1.05ny > nz > nx 6 80 245 0.041 1.12 nx > ny > nz 125 65 231 Ex. 2 132 −102−100 1.06 ny > nz > nx 10.5 25 390 0.037 1.12 nx > ny > nz 162.5 −77 290Ex. 3 40 −218 −109 1.09 ny > nz > nx 9 62 360 0.040 1.12 nx > ny > nz 69−156 251 Comp. 95 28 52 1.01 nx > ny > nz 5.6 37 220 0.042 1.12 nx >ny > nz 100.6 65 272 Ex. 1 Comp. 83 49 118 1.01 nx > ny > nz — — — — — —83 49 118 Ex. 2 Comp. 90 53 1.2 1.05 ny > nz > nx — — — — — — 90 53 1.2Ex. 3 Comp. — — — — 6 60 240 0.04 1.02 nx > ny > nz 6 60 240 Ex. 4

(Evaluation of Panel Viewing Angle Property)

Each of the birefringent optical films obtained in Examples 1 to 3 andComparative Examples 1 to 4 was bonded to a polarizing plate (tradename: SEG1425DU, manufactured by Nitto Denko Corporation) via an acrylicpressure sensitive adhesive layer (20 tm in thickness), thus obtaining alaminated polarizing plate. In the laminated polarizing plate, thebirefringent optical film was arranged so that the birefringent B-layerincluded therein faced the polarizing plate. The thus-obtained laminatedpolarizing plate and a polarizing plate (trade name: SEG1425DU,manufactured by Nitto Denko Corporation) respectively were disposed onboth surfaces of a VA type liquid crystal liquid crystal cell so thatthe slow axes of the respective polarizing plates are orthogonal to eachother, thus obtaining a liquid crystal display. The laminated polarizingplate was arranged on the rear side of the liquid crystal cell so thatthe polarizing plate included therein came in contact with the liquidcrystal cell.

Next, for the thus-obtained respective liquid crystal displays, viewingangles at contrast ratios of (Co)≧10 in a vertical direction, in alateral direction, in a diagonal direction (45° to 225° ) and in adiagonal direction (135° to 315° ) were measured. The contrast ratioswere obtained by, displaying a white image and a black image on each ofthe liquid crystal displays, for measuring the values of Y, x, and y ina XYZ display system at viewing angles of 0-70° at the front, upper,lower, right and left sides of the display, by using an instrument(trade name: Ez contrast 160D, manufactured by ELDIM SA.). Based on theY-value (Y_(W)) for the white image and the Y-value (Y_(B)) for theblack image, the contrast ratio (Y_(W)/Y_(B)) for every viewing anglewas calculated. The viewing angle property was evaluated as “Good” whenan omnidirectional contrast was 10 or more, while “Bad” indicates thatthe omnidirectional contrast was lower than 10. The results are shown inTable 2.

(Evaluation of Panel Coloring Prevention)

The liquid crystal displays obtained in the above-described manner wereevaluated visually based on the following criteria.

Excellent: no coloring was observed at all

Good: although some coloring was observed, such coloring was allowablein practical use.

Bad: coloring unallowable in practical use was observed.

The results are shown in Table 2. TABLE 2 Panel viewing Prevention ofangle property panel coloring Front contrast Ex. 1 Good Good 840 Ex. 2Good Excellent 830 Ex. 3 Good Excellent 700 Comp. Ex. 1 Good Bad 320Comp. Ex. 2 Bad Bad 280 Comp. Ex. 3 Bad Bad 850 Comp. Ex. 4 Good Bad 600

As shown in Table 2, each birefringent optical film of the presentinvention could allow the liquid crystal display incorporating the filmto achieve excellent contrast and a wide viewing angle and did not causecoloring.

INDUSTRIAL APPLICABILITY

As specifically described above, a birefringent optical film of thepresent invention allows a liquid crystal display to achieve excellentcontrast and a wide viewing angle and does not cause coloring of theliquid crystal display.

1. A birefringent optical film comprising: at least one birefringentA-layer; and at least one birefringent B-layer, wherein the birefringentA-layer has a property satisfying ny_(a)≧nz_(a)>nx_(a) ornz_(a)>ny_(a)≧nx_(a), and the birefringent B-layer has a propertysatisfying nx_(b)≧ny_(b)>nz_(b), where nx_(a), ny_(a) and nz_(a)respectively represent refractive indices in an X-axis direction, aY-axis direction, and a Z-axis direction in the birefringent A-layer,with the X-axis direction being an axial direction that is the same as abelow-mentioned X-axis direction of the birefringent B-layer, the Y-axisdirection being an axial direction that is the same as a below-mentionedY-axis direction of the birefringent B-layer, and the Z-axis directionbeing a thickness direction perpendicular to the X axis and the Y axis,and nx_(b), ny_(b) and nz_(b) respectively represent refractive indicesin the X-axis direction, the Y-axis direction, and a Z-axis direction inthe birefringent B-layer, with the X-axis direction being an axialdirection exhibiting a maximum refractive index within a plane of thebirefringent B-layer, the Y-axis direction being an axial directionperpendicular to the X axis within the plane, and the Z-axis directionbeing a thickness direction perpendicular to the X axis and the Y axis.2. The birefringent optical film according to claim 1, wherein thebirefringent B-layer meets a requirement represented by a formula (1)below,0.005≦Δn_(b)≦0.2  (1) where Δn_(b) is nx_(b)−nz_(b), and nx_(b) andnz_(b) respectively represent the refractive indices in the X-axisdirection and the Z-axis direction in the birefringent B-layer, with theX-axis direction being the axial direction exhibiting the maximumrefractive index within the plane of the birefringent B-layer and theZ-axis direction being the thickness direction perpendicular to theX-axis.
 3. The birefringent optical film according to claim 1, whereinthe birefringent A-layer is formed of at least one of a polymerexhibiting negative birefringence and a polymer exhibiting positivebirefringence.
 4. The birefringent optical film according to claim 3,wherein the birefringent A-layer is formed of a mixture of the polymerexhibiting negative birefringence and the polymer exhibiting positivebirefringence.
 5. The birefringent optical film according to claim 1,wherein the birefringent B-layer is formed of a polymer exhibitingpositive birefringence.
 6. The birefringent optical film according toclaim 5, wherein the polymer exhibiting positive birefringence is atleast one polymer selected from the group consisting of polyamide,polyimide, polyester, polyetherketone, polyaryletherketone, polyamideimide and polyesterimide.
 7. The birefringent optical film according toclaim 1, meeting a requirement represented by a formula (4) below,−3°≦alignment axis accuracy≦3°  (4) where the alignment axis accuracyrefers to variation in slow axis within a plane of the birefringentoptical film.
 8. The birefringent optical film according to claim 1,wherein an in-plane retardation of the birefringent optical film hasreciprocal wavelength dispersion characteristics.
 9. The birefringentoptical film according to claim 1, meeting requirements represented byformulae (5) and (6) below,|Δand_(a)|>|Δnd_(b)|  (5)α_(a)<α_(b)  (6) in the formulae (5) and (6),Δnd_(a)=(nx_(a)−ny_(a))·d_(a), Δnd_(b)=(nx_(b)−ny_(b))·d_(b),α_(a)=Δnd_(a430 nm)/Δnd_(a550 nm), andα_(b)=Δnd_(b430 nm)/Δnd_(b550 nm), where nx_(a) and ny_(a) respectivelyrepresent the refractive indices in the X-axis direction and the Y-axisdirection in the birefringent A-layer, with the X-axis direction beingthe axial direction that is the same as the X-axis direction of thebirefringent B-layer and the Y-axis direction being the axial directionthat is the same as the Y-axis direction of the birefringent B-layer,and d_(a) represents a thickness of the birefringent A-layer, nx_(b) andny_(b) respectively represent the refractive indices in the X-axisdirection and the Y-axis direction in the birefringent B-layer, with theX-axis direction being the axial direction exhibiting the maximumrefractive index within the plane of the birefringent B-layer and theY-axis direction being the axial direction perpendicular to the X-axiswithin the plane, and d_(b) represents a thickness of the birefringentB-layer, Δnd_(a430 nm) and Δnd_(a550 nm) respectively represent Δnd_(a)values of the birefringent A-layer at wavelengths of 430 nm and 550 nm,and Δnd_(b430 nm) and Δnd_(b550 nm) respectively represent Δnd_(b)values of the birefringent B-layer at the wavelengths of 430 nm and 550nm.
 10. A laminated polarizing plate comprising a birefringent opticalfilm, wherein the birefringent optical film is the birefringent opticalfilm according to claim
 1. 11. A liquid crystal panel comprising aliquid crystal cell and an optical member, the optical member beingdisposed on at least one surface of the liquid crystal cell, wherein theoptical member is the birefringent optical film according to claim 1 ora laminated polarizing plate comprising the birefringent optical filmaccording to claim
 1. 12. A liquid crystal display comprising a liquidcrystal panel, wherein the liquid crystal panel is the liquid crystalpanel according to claim
 11. 13. An image display comprising thebirefringent optical film according to claim 1 or a laminated polarizingplate comprising the birefrinient optical film according to claim
 1. 14.The birefringent optical film according to claim 4, wherein the polymerexhibiting negative birefringence and the polymer exhibiting positivebirefringence contained in the mixture for forming the birefringentA-layer are compatible with each other.
 15. The birefringent opticalfilm according to claim 1, comprising one birefringent A-layer and oneto three birefringent B-layers.
 16. The birefringent optical filmaccording to claim 1, wherein the birefringent A-layer is formed of atleast one of a polymer exhibiting negative birefringence and a polymerexhibiting positive birefringence, and the birefringent B-layer isformed of a polymer exhibiting positive birefringence.